The transfer block (note cutout chest) of a Wurlitzer 150 with a duplex
frame is as John Rutoskey mentioned: a pouch for each note on each
trackerbar.

The two sets of pouches are separated in their own chambers, operated
by a mechanical lock and cancel as I recall, which in turn is switched
back and forth by the roll switching mechanism.  When one chamber is
switched to vacuum, the other is switched to air, cutting it off.  Here
is occasionally a problem, too.  The switch doesn't go far enough over
to adequately cut one side off and the other side on.

If you decide to replace the cutout pouches in a Wurlitzer 150 cutout
stack, it is important to seal and talc those pouches on their slick
side.  The vacuum supply in these instruments are marginal anyway on
a busy roll with lots of notes.  The vacuum reservoir _should_ be
spilling most of the time.  If you notice that your reservoir almost
never spills, or doesn't spill as much when it switches to the spool
frame that gives you a problem, then this could indicate what your
trouble is. low vacuum, due to one side or the other of the duplex
cutout stack.  Substitute another vacuum supply, greater than that in
the reservoir, and try it.

For instance, a leaky chamber, hose, nipple, or generally ciphering
pouches in concert can also cause your problem by weakening the overall
vacuum so that marginal valves aren't working well, anymore.  That
would mean your cutout chest could have a leak on the side that's
supposed to be cutting out.

All the other suggestions given I would agree with, too.  But I would
begin with a test roll as Don Teach mentioned.  Prevent the roll from
traveling, so you can advance it by hand.  On the bad notes, try
bypassing the cutout stack if possible (a "Y" and a piece of tubing
around the cutout stack.  Then put the test roll on the other spool
frame and try the same thing.

Have a good vacuum gauge always on the supply with a fixed leak to air
to simulate more notes playing, first.  Then when you test for the bad
notes, you might learn something about your supply vacuum or the
different sides of the cutout stack.  This was something I didn't see
discussed.

Dirt and dust under the cutout pouch usually causes the notes to play
when you don't want them to.  Notes that don't play when you want them
to are usually caused either by stuck pouches, plugged trackerbar
lines, or weak cutout chest vacuum that doesn't allow marginal c/o
pouches to lift enough, or marginal pipe valves to operate.

So test the cutout supply vacuum first, and then once you're certain
that works and doesn't leak, go for the individual note lines.

Craig Brougher